The Fairs cup was played for by teams from cities where the trade fairs were held during the 60’s. Teams didn’t qualify by league position.The Fairs Cup was a strange competition. The first edition was played over two or three seasons and featured a London select side.
There was a rule that only teams from Cities could qualify and I think only one team per City (hence the London select team).
By the late 1960s and early 1960s, it was probably on a par with the Cup Winners Cup. By the time it was rebadged as the UEFA Cup, some felt it was harder to win than the European Cup.